reCAPTCHA

reCAPTCHA is a CAPTCHA-like system designed to establish that a computer user is human and, at the same time, assist in the digitization of books. reCAPTCHA was originally developed by Luis von Ahn, Ben Maurer, Colin McMillen, David Abraham and Manuel Blum at Carnegie Mellon University's main Pittsburgh campus. It was acquired by Google in September 2009.